From EP 1 167 140 A2 a wheel drive of this type is known, in which both a driving brake and a parking brake are integrated. Here, the parking brake is provided on the side of the drive input of the planetary gearbox and is effective between a stationary carrying axle on the one hand and a sun gear shaft of the planetary gearbox on the other. The driving brake, however, is arranged on the side of the drive output of the planetary gearbox and is effective between the ring gear also serving as a gear hub on the one hand and the correspondingly extended carrying axle on the other. Each brake is driven by a hydraulic cycle and each essentially comprises a disk package which is actuated by a pressure spring in the case of the parking brake and by means of a pressurized medium in the case of the driving brake. The incorporation of both the driving brake and the parking brake in the wheel drive needs considerable structural space, in particular due to the two disk packages, each having their associated actuating means.
From EP 0 913 304 A2 a wheel drive is known, in which this drawback is eliminated in that a common disk package is provided for both the driving brake and the parking brake. The disk package is operated by means of a separate hydraulic cycle for the driving brake and by means of another, separately formed, hydraulic cycle for the parking brake. However, both hydraulic cycles act on one and the same piston to compress the disk package for braking.
A drawback of this approach is that such a common operation of the single braking piston is a security hazard, since a system redundancy is largely done without. If the common brake piston fails, the functioning of the brake is no longer ensured, even if it is driven by means of the other hydraulic cycle. Moreover, according to statutory regulations in many countries, a parking brake without a spring action is not allowed.